1. Field of the Invention
The present invention relates to a thin film transistor (TFT) for a flat panel display (FPD) device, and more particularly, to a multi-channel type TFT and a method of fabricating the same that can prevent deterioration thereof.
2. Discussion of the Related Art
Recently, FPD devices, which includes liquid crystal display (LCD) devices, are manufactured as large-size display devices that have high resolution due to implementation of semiconductor devices in the FPD devices.
In general, the LCD devices use optical anisotropy and polarization properties of liquid crystal molecules in order to display images. The liquid crystal molecules have a definite orientational alignment resulting from their thin and long shapes, wherein the alignment direction of the liquid crystal molecules can be controlled by application of an electric field to the liquid crystal molecules. Accordingly, as an intensity of the applied electric field is changed, the alignment of the liquid crystal molecules also changes. Since incident light through liquid crystals within the liquid crystal molecules is refracted based upon an orientation of the liquid crystal molecules, intensity of the incident light can be controlled and images can be displayed due to the optical anisotropy of the aligned liquid crystal molecules.
Among the various types of LCD devices commonly used, active matrix LCD (AM-LCD) devices have been developed because of their high resolution and superiority in displaying moving images. The AM-LCD devices have TFTs and pixel electrodes connected to the TFTs disposed in matrix configuration. The TFTs include polysilicon material having a higher field efficiency mobility than amorphous silicon material that is sensitive to light or to electric fields when the polysilicon material is utilized for a driving integrated circuit element, i.e., the TFT element. Accordingly, the polysilicon TFT can reduce costs of the driving integrated circuit and can help simplify device packaging when the polysilicon material is directly formed on a substrate as the driving integrated circuit.
The polysilicon TFT can minimize current loss of an ON state to provide a fast mobility speed of the driving IC and pixels, and has a relatively low power consumption. In addition, a lightly doped drain (LDD) region, which is treated with impurities of a lower concentration than the n+ or p+ doping concentrations of the source/drain regions that prevent leakage current increase, is defined in the polysilicon TFT. Furthermore, the electric field of a drain electrode of the TFT can be reduced by the LDD region having a low consistency, thereby reducing deterioration of the device by hot carriers.
FIG. 1 is a schematic plan view of a multi-channel type TFT according to the related art. The multi-channel type TFT 50 of FIG. 1 is manufactured in order to increase driving power and to prevent deterioration due to self-heating. In FIG. 1, a gate electrode 26 is formed over a substrate (not shown) to extend along a first direction, and source and drain electrodes 34 and 38 are spaced apart from each other with respect to the gate electrode 26 and extend along the first direction. A plurality of active layers ACT1 to ACT2N (N is defined a positive fixed number) are disposed parallel to and spaced apart from each other along a second direction crossing the first direction, wherein each of the plurality of active layers ACT1 to ACT2N includes a channel region CR overlapped with the gate electrode 26, a source region SR, a drain region DR, and lightly doped drain (LDD) regions LR; one between the channel region CR and the source region SR and another one between the channel region CR and the drain region DR. Here, the plurality of active layers ACT1 to ACT2N include a polysilicon material. However, a distance D1 between adjacent active layers ACT1 to ACT2N are limited since a size of an integrated circuit is limited by an integrated characteristic of a high density of the LCD although a width W1 of each of the active layers ACT1 to ACT2N is widened. As a result, the layout of the multi-channel type TFT is limited.
FIG. 2 is a graphic illustration of heating values of channel regions of the multi-channel TFT of FIG. 1 according to the related art. In FIG. 2, a central portion CP of the multi-channel type TFT 50 has a bigger disadvantage than edge portions EP thereof since a space of the heat diffusion and a route of the heat diffusion are both relatively narrow. In general, cooling in the central portion CP is more difficult than in the edge portions EP.
FIG. 3 is a photomicrograph of a central portion of the multi-channel type TFT according to the related art. In FIG. 3, the multi-channel type TFT has a significant disadvantage, such as deterioration due to self-heating. Therefore, since its cost increases, productivity is reduced.